Isaac sim pose tree problem

Is the first two links in pose tree are reversed?

If a robot is defined like y_branch as below, the first two links are reversed in ROS.
y_branch_fail.pdf (13.7 KB)

The pdf file states the relation of urdf. The png file is the result captured from omniverse and rviz(visualization software of ROS), the yellow box shows the tf tree read by ROS.

I used isaac sim with ROS and found that the first two links are reversed. I tested this issue with three cases: Single_branch, two_branch, and y_branch. In the file y_branch_fail.png, it shows that link2 is the child of world (highlighted in yellow) while in the file y_branch_fail.urdf link1 is the child of world and link2 is the child of link1 (highlighted in yellow).

two_branch.pdf (13.3 KB)

single_branch.pdf (12.9 KB)

Can you upload the urdf in question so we can look into it? Thanks.

single_branch.urdf (260 Bytes)
two_branch.urdf (471 Bytes)
y_branch_fail.urdf (679 Bytes)

Attached the urdf, Thanks!

The urdf provided seems to work for me. Which version of Isaac Sim are you running? Is there any chance you can upgrade to our latest release?

I updated to the latest release 2021.2.0, but the problem is still here.
Please unselect “Fix Base Link”

ah, yes, unfix the base breaks it. We’ll look into it. Thanks for letting us know!

1 Like


We filed a bug for it. But for now, you can fix it by manually change where you put the articulation root. When you imported it through the urdf importer, it automatically added an “articulation root” on the main robot prim, and that’s causing issues. You can delete the articulation root from your “test_robot” prim, and then add one to your link 1.

  1. Select test_robot (or whatever your robot’s name is) on the stage tree, go to the property tab, find the “Articulation Root” section, and delete it by click on the x.
  2. Select link 1, go to the property tab, click on the the +Add button and select Phyics->Articulation Root